Correlation between electrochemical behavior and hydrogen storage properties of Li–Sn system

• The destabilization of LiH through Li insertion into Sn has been studied.
• The highest Li containing phase is confirmed to be Li17Sn4 instead of Li22Sn5.
• The enthalpies of formation for 1st and 2nd step reaction are -93 and -37 kJ/molH2.
• A correlation between hydrogenation and electrochemical properties is established.

The high stability of Lithium hydride is a bottleneck to use it as hydrogen storage media. The present paper is an effort to destabilize it using Sn as a dopant. Li4.4Sn is chosen due to its highest lithium content among all the possible stoichiometries. It is found that the real composition is Li17Sn4 rather than Li4.4Sn. Hydrogenation measurements suggest the existence of two step reaction. Li17Sn4 first react with hydrogen to form a mixture of LiH and Li13Sn5, which further transformed into a mixed phase of LiSn and LiH as final product under studied hydrogenation condition. The enthalpy values for the above mentioned reactions are found to be −93 ± 11 kJ/mol H2 and −37 ± 2 kJ/mol H2 for 1st and 2nd step respectively. These values are much lower than the values observed for pure LiH. Finally these hydrogenation properties were used to calculate the electrochemical potential values required for lithiation/delithiation. The value for potential for 1st step and 2nd step reaction is found to be 0.456 V and 0.746 V for Li–Sn system, which is in good agreement with the values calculated through direct electrochemical methods.